DCN-IP

IPV4 vs IPV6

	IPv4	IPv6
Address	32 bits (4 bytes) 12:34:56:78	128 bits (16 bytes) 1234:5678:9abc:def0: 1234:5678:9abc:def0
Packet size	576 bytes required, fragmentation optional	1280 bytes required without fragmentation
Packet fragmentation	Routers and sending hosts	Sending hosts only
Packet header	Does not identify packet flow for QoS handling	Contains Flow Label field that specifies packet flow for QoS handling
	Includes a checksum	Does not include a checksum
	Includes options up to 40 bytes	Extension headers used for optional data
DNS records	Address (A) records, maps host names	Address (AAAA) records, maps host names
	Pointer (PTR) records, IN-ADDR.ARPA DNS domain	Pointer (PTR) records, IP6.ARPA DNS domain
Address configuration	Manual or via DHCP	Stateless address autoconfiguration (SLAAC) using Internet Control Message Protocol version 6 (ICMPv6) or DHCPv6
IP to MAC resolution	broadcast ARP	Multicast Neighbor Solicitation
Local subnet group management	Internet Group Management Protocol (IGMP)	Multicast Listener Discovery (MLD)
Broadcast	Yes	No
Multicast	Yes	Yes
IPSec	optional, external	required

IPv4 Addressing system is divided into five classes of IP Addresses. All the five classes are identified by the first octet of IP Address.

Internet Corporation for Assigned Names and Numbers is responsible for assigning IP addresses.

The first octet referred here is the left most of all. The octets numbered as follows depicting dotted decimal notation of IP Address:

 

The number of networks and the number of hosts per class can be derived by this formula:

 

When calculating hosts' IP addresses, 2 IP addresses are decreased because they cannot be assigned to hosts, i.e. the first IP of a network is network number and the last IP is reserved for Broadcast IP.

Class A Address

The first bit of the first octet is always set to 0 (zero). Thus the first octet ranges from 1 – 127, i.e.

00000001-01111111

1-127

Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only.

·        127.x.x.x is reserved for loopback IP addresses.

·        The default subnet mask for Class A IP address is 255.0.0.0 which implies that Class A addressing can have 126 networks (2⁷-2) and 16777214 hosts (2²⁴-2).

Class A IP address format is thus: 0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH

Class B Address

An IP address which belongs to class B has the first two bits in the first octet set to 10, i.e.

10000000-10111111

128-191

·        Class B IP Addresses range from 128.0.x.x to 191.255.x.x.

·        The default subnet mask for Class B is 255.255.x.x.

·        Class B has 16384 (2¹⁴) Network addresses and 65534 (2¹⁶-2) Host addresses.

Class B IP address format is: 10NNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH

Class C Address

The first octet of Class C IP address has its first 3 bits set to 110, that is:

11000000-110111111

192-223

·        Class C IP addresses range from 192.0.0.x to 223.255.255.x.

·        The default subnet mask for Class C is 255.255.255.x.

·        Class C gives 2097152 (2²¹) Network addresses and 254 (2⁸-2) Host addresses.

Class C IP address format is: 110NNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

Class D Address

Very first four bits of the first octet in Class D IP addresses are set to 1110, giving a range of:

11100000-11101111

224-239

·        Class D has IP address rage from 224.0.0.0 to 239.255.255.255.

·        Class D is reserved for Multicasting. In multicasting data is not destined for a particular host, that is why there is no need to extract host address from the IP address,

·        Class D does not have any subnet mask.

Class E Address

·        This IP Class is reserved for experimental purposes only for R&D or Study.

·         IP addresses in this class ranges from 240.0.0.0 to 255.255.255.254.

·         Like Class D, this class too is not equipped with any subnet mask.

There are a few reserved IPv4 address spaces which cannot be used on the internet. These addresses serve special purpose and cannot be routed outside the Local Area Network.

Private IP Addresses

Every class of IP, (A, B & C) has some addresses reserved as Private IP addresses. These IPs can be used within a network, campus, company and are private to it. These addresses cannot be routed on the Internet, so packets containing these private addresses are dropped by the Routers.

 

In order to communicate with the outside world, these IP addresses must have to be translated to some public IP addresses using NAT process, or Web Proxy server can be used.
The sole purpose to create a separate range of private addresses is to control assignment of already-limited IPv4 address pool. By using a private address range within LAN, the requirement of IPv4 addresses has globally decreased significantly. It has also helped delaying the IPv4 address exhaustion.
IP class, while using private address range, can be chosen as per the size and requirement of the organization. Larger organizations may choose class A private IP address range where smaller organizations may opt for class C. These IP addresses can be further sub-netted and assigned to departments within an organization.

Loopback IP Addresses

The IP address range 127.0.0.0 – 127.255.255.255 is reserved for loopback, i.e. a Host’s self-address, also known as localhost address. This loopback IP address is managed entirely by and within the operating system. Loopback addresses, enable the Server and Client processes on a single system to communicate with each other. When a process creates a packet with destination address as loopback address, the operating system loops it back to itself without having any interference of NIC.
Data sent on loopback is forwarded by the operating system to a virtual network interface within operating system. This address is mostly used for testing purposes like client-server architecture on a single machine. Other than that, if a host machine can successfully ping 127.0.0.1 or any IP from loopback range, implies that the TCP/IP software stack on the machine is successfully loaded and working.

Link-local Addresses

In case a host is not able to acquire an IP address from the DHCP server and it has not been assigned any IP address manually, the host can assign itself an IP address from a range of reserved Link-local addresses. Link local address ranges from 169.254.0.0 -- 169.254.255.255.
Assume a network segment where all systems are configured to acquire IP addresses from a DHCP server connected to the same network segment. If the DHCP server is not available, no host on the segment will be able to communicate to any other. Windows (98 or later), and Mac OS (8.0 or later) supports this functionality of self-configuration of Link-local IP address. In absence of DHCP server, every host machine randomly chooses an IP address from the above mentioned range and then checks to ascertain by means of ARP, if some other host also has not configured itself with the same IP address. Once all hosts are using link local addresses of same range, they can communicate with each other.
These IP addresses cannot help system to communicate when they do not belong to the same physical or logical segment. These IPs are also not routable.

IPv4 supports three different type of addressing modes:

Unicast Addressing Mode:

In this mode, data is sent only to one destined host. The Destination Address field contains 32- bit IP address of the
destination host. Here client sends data to the targeted server:

Broadcast Addressing Mode:In this mode the packet is addressed to all hosts in a network segment. The 

Destination Address field contains special broadcast address i.e. 255.255.255.255. When a host sees this packet on 

the network, it is bound to process it. Here client sends packet, which is entertained by all the Servers:

 

 

Multicast Addressing Mode:This mode is a mix of previous two modes, i.e. the packet sent is neither

 destined to a single host nor all the host on the segment. In this packet, the Destination Address contains special 

address which starts with 224.x.x.x and can be entertained by more than one host. 

Here a server sends packets which are entertained by more than one Servers.
Every network has one IP address reserved for network number which represents
the network and one IP address reserved for Broadcast Address, which represents
all the host in that network.